I hate to say it but yes being 1 inch lower in the water can be very significant. Of course the boat will never sink when you pile the weight on but it will start to display other undesireable behavior. Examples are ; wave slapping with the back beam (BIM A-cats, older F18HT's, Nacra 500 with lots of weight) or taking the chop on the mainbeam (Taipan 4.9 when 2-up and heavy). The boat can also get very weight sensitive and allow backward flipping when tacking (Hobie 16). Or bad dive resistance.

Interestingly enough all these issue are associated with too little volume in the hulls, never with too much volume. That is one of the reason for my earlier statement that it is relative hard to overdo it with respect to volume.

Wouter